The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year.
The world energy consumption in 2010 was 474 exajoules.
Obviously energy consumption would need to massively increase since all food would need to be grown by artifical light, as would all light that humans/animals would recieve, but I figure that by the point that humanity covers all of the land and all of the water with solar panels, then organics won't be really very common anyways.
Now, assuming that the atmosphere absorbs 50% of that, and regular land+sea based arrays would be able to capture the other 50%, that's 4,060 times the current energy consumption (although at the point where every square inch of earth was covered by solar panels, we would probably start to use space-based solar sources, so that's by no means the upper bound of energy production).
Sand. Sand would definitely be a problem.
...Well yes, but not an insurmountable one. It'd probably go under "cost".
It's quite the barrier for space-based arrays, and that's where there's relatively few fine particulates (compared to a desert). It's a big problem. One that still requires a bit of research to overcome.
I do think that's mainly because the particles in space are going at like 5 miles per second, which isn't a problem in a desert.